PS9-2. Association Between Temperament and Serum Metabolomics in Feedlot Nellore Cattle.

Abstract Pre-slaughter stress alters systemic metabolism in cattle and can influence physiological processes related to meat quality. Circulating metabolites, such as lactate and amino acids, may reflect metabolic responses to stress and energy metabolism. The objective of this study was to evaluate the association between cattle excitability and blood metabolite profiles collected at exsanguination in feedlot cattle. Thirty-four non-castrated Nelore steers (18 ± 2 months old) were confined for 74 days and fed a diet containing a 75:25 concentrate-to-forage ratio. Temperament index was determined as the average of chute score (CS) and exit velocity (EV), evaluated on day 37 of the feedlot period, and used to classify animals as calm (CAL; n = 17) or excitable (EXC; n = 17). On the day of slaughter, animals were loaded in the morning and transported approximately 300 meters to the University of Sao Paulo teaching abattoir. Blood was collected at exsanguination and, after centrifugation, the obtained serum was filtered using 3 kDa ultrafiltration filters at 10,000 × g for 30 minutes at 4 °C. The collected supernatant was analyzed using nuclear magnetic resonance (¹H-NMR). Univariate statistical analyses were performed independently for each metabolite using linear models to evaluate treatment effects in an exploratory approach. The ¹H-NMR analysis identified 44 metabolites common to both treatments. EXC animals exhibited greater concentrations of proline and lactate compared to CAL animals (P = 0.017 and P = 0.038, respectively), while CAL animals showed greater serine levels than EXC animals (P = 0.029). Greater serine concentrations in CAL animals may indicate a more regulated metabolic state, as serine participates in pathways associated with cellular homeostasis and redox balance. In contrast, EXC animals appear to exhibit stronger metabolic responses to stress, as indicated by elevated lactate, reflecting enhanced glycolytic activity, and higher proline which may be linked to amino acid metabolism and cellular stress responses. These metabolic alterations may influence postmortem biochemical processes relevant to meat quality, potentially reducing beef quality in EXC animals.